1. Field of the Invention
The present invention relates to an optical near-field generating device, a magnetic recording head including an optical near-field generating unit, and a magnetic recording device using the same.
2. Description of the Related Art
A thermally assisted recording method has recently been proposed as a recording method for achieving a recording density of 1 Tb/in2 or higher (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys., 38, Part 1, 1839 (1999)). With a recording density of 1 Tb/in2 or higher, conventional magnetic recording devices have a problem that thermal fluctuations destroy recorded information. The prevention of this requires enhancement of coercivity of a magnetic recording medium. Too high a coercivity, however, makes it impossible to form a recording bit on the medium because there is a limit to the magnitude of a magnetic field that a recording head can generate. To address this, the thermally assisted recording method involves heating the medium with light, thereby reducing the coercivity at the instant of recording. This makes it possible to perform recording on media with high coercivity, and thus to achieve a recording density of 1 Tb/in2 or higher.
For the thermally assisted recording device, it is necessary that the spot diameter of light to be radiated be substantially equivalent to the size of the recording bit (e.g., several 10 nm). The reason is that the spot diameter of light in excess of several 10 nm erases information on an adjacent track. To heat such a minute region, an optical near-field is used. The optical near-field is a localized electromagnetic field (the light whose wave number has imaginary components) that is present in the vicinity of a minute object whose size is equal to or smaller than wavelengths of light. A microaperture having a diameter equal to or smaller than the wavelengths of light or a metal scatterer is used to generate the optical near-field. For example, JP2001-255254A proposes an optical near-field generating unit using a metal scatterer of a triangular shape as a high-efficiency optical near-field generating unit. When light is made incident on the metal scatterer, plasmon resonance is excited in the metal scatterer, and a strong optical near-field is generated at an apex of the triangle. Using this optical near-field generating unit makes it possible to focus light with high efficiency on a region equal to or smaller than several 10 nm. Meanwhile, JP2004-151046A proposes a structure in which a surface, on a slider floating surface side, of the metal scatterer is shaved to form a dent in a portion other than the apex where the optical near-field is generated. This structure can reduce the width of intensity distribution of the optical near-field generated at the apex, and thus can suppress generation of a weak optical near-field (background light) generated on the side opposite to the apex.    Patent Document 1: JP2001-255254A    Patent Document 2: JP2004-151046A    Non-Patent Document 1: Jpn. J. Appl. Phys., 38, Part 1, 1839 (1999)